Network Working Group Srihari R. Sangli (Procket Networks)
Internet Draft Daniel Tappan (Cisco Systems)
Expiration Date: November 2002February 2004 Yakov Rekhter (Juniper Networks)
BGP Extended Communities Attribute
draft-ietf-idr-bgp-ext-communities-05.txtdraft-ietf-idr-bgp-ext-communities-06.txt
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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2. Abstract
This document describes an extension to BGP-4 which may be used to
provide flexible control over the distribution of routing
information.
3. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
4. Introduction
The Extended Community Attribute provides two important enhancements
over the existing BGP Community Attribute:
- It provides an extended range, ensuring that communities can be
assigned for a plethora of uses, without fear of overlap.
- The addition of a Type field provides structure for the
community space.
The addition of structure allows the usage of policy based on the
application for which the community value will be used. For example,
one can filter out all communities of a particular type, or allow
only certain values for a particular type of community. It also
allows one to specify whether a particular community is transitive or
non-transitive across Autonomous system boundary. Without structure,
this can only be accomplished by explicitly enumerating all community
values which will be denied or allowed and passed to BGP speakers in
neighboring ASes based on the transitive property.
5. BGP Extended Communities Attribute
The Extended Communities Attribute is a transitive optional BGP
attribute, with the Type Code 16. The attribute consists of a set of
"extended communities". All routes with the Extended Communities
attribute belong to the communities listed in the attribute.
Each Extended Community is encoded as an eight octet quantity, as
follows:
- Type Field : 1 or 2 octets
- Value Field : Remaining octets
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type high | Type low(*) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Value |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*) Present for Extended types only, used for the Value field
otherwise
Type Field:
Two classes of Type Field are introduced: Regular type and
Extended type.
The size of Type Field for Regular types is 1 octet and the
size of the Type Field for Extended types is 2 octets.
The value of the high-order octet of the Type Field determines
if an extended community is a Regular type or an Extended type.
The high-order octet of the Type Field is as shown below:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|I|T| |
+-+-+-+-+-+-+-+-+
I - IANA authority bit
Value 0: IANA assignable type using the "First Come First
Serve" policy
Value 1: IANA assignable type using the IETF Consensus
policy and experimental
T - Transitive bit
Value 0: The community is transitive across ASes
Value 1: The community is non-transitive across ASes
Remaining 6 bits: Indicates the structure of the community
Value Field:
The encoding of the Value Field is dependent on the "type" of
the community as specified by the Type Field.
Two extended communities are declared equal only when all 8 octets of
their encoding are equal.
The two members in the tuple <Type, Value> should be enumerated to
specify any community value. Based on the value of the Type field,
the remaining octets of the community should be interpreted.
6. Defined BGP Extended Community Types
This section introduces a few extended types and defines the format
of the Value Field for those types. The types introduced here provide
"templates", where each template is identified by the high order
octet of the extended community Type field, and the lower order octet
(sub-type) is used to indicate a particular type of extended commu-
nity.
6.1. Two-octet AS specific extended community
This is an extended type with Type Field comprising of 2 octets and
Value Field comprising of 6 octets.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x00 or 0x40 | Sub-Type | Global Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The value of the high-order octet of this extended type is either
0x00 or 0x40. The low-order octet of this extended type is used to
indicate sub-types.
The Value Field consists of two sub-fields:
Global Administrator sub-field: 2 octets
This sub-field contains an Autonomous System number assigned by
IANA.
Local Administrator sub-field: 4 octets
The organization identified by Autonomous System number in the
Global Administrator sub-field, can encode any information in
this sub-field. The format and meaning of the value encoded in
this sub-field should be defined by the sub-type of the commu-
nity.
6.2. IPv4 address specific extended community
This is an extended type with Type Field comprising of 2 octets and
Value Field comprising of 6 octets.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x01 or 0x41 | Sub-Type | Global Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Administrator (cont.) | Local Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The value of the high-order octet of this extended type is either
0x01 or 0x41. The low-order octet of this extended type is used to
indicate sub-types.
The Value field consists of two sub-fields:
Global Administrator sub-field: 4 octets
This sub-field contains an IPv4 address assigned by IANA.
Local Administrator sub-field: 2 octets
The organization which has been assigned the IPv4 address in
the Global Administrator sub-field, can encode any information
in this sub-field. The format and meaning of this value
encoded in this sub-field should be defined by the sub-type of
the community.
6.3. Four-octet AS specific extended community
This is an extended type with Type Field comprising of 2 octets and
Value Field comprising of 6 octets.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x02 or 0x42 | Sub-Type | Global Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Global Administrator (cont.) | Local Administrator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The value of the high-order octet of this extended type is either
0x02 or 0x42. The low-order octet of this extended type is used to
indicate sub-types.
The Value Field consists of two sub-fields:
Global Administrator sub-field: 4 octets
This sub-field contains a 4-octets Autonomous System number
assigned by IANA.
Local Administrator sub-field: 2 octets
The organization identified by Autonomous System number in the
Global Administrator sub-field, can encode any information in
this sub-field. The format and meaning of the value encoded in
this sub-field should be defined by the sub-type of the commu-
nity.
6.4. Opaque extended community
This is an extended type with Type Field comprising of 2 octets and
Value Field comprising of 6 octets.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x03 or 0x43 | Sub-Type | Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The value of the high-order octet of this extended type is either
0x03 or 0x43. The low-order octet of this extended type is used to
indicate sub-types.
This is a generic community of extended type. The value of the sub-
type which should define the Value Field is to be assigned by IANA.
7. Route Target Community
The Route Target Community identifies one or more routers that may
receive a set of routes (that carry this Community) carried by BGP.
This is transitive across the Autonomous system boundary.
The Route Target Community is of an extended type.
The value of the high-order octet of the Type field for the Route
Target Community can be 0x00, 0x01 or 0x02. The value of the low-
order octet of the Type field for this community is 0x02.
When the value of the high-order octet of the Type field is 0x00 or
0x02, the Local Administrator sub-field contains a number from a num-
bering space which is administered by the organization to which the
Autonomous System number carried in the Global Administrator subfield
has been assigned by an appropriate authority.
When the value of the high-order octet of the Type field is 0x01, the
Local Administrator sub-field contains a number from a numbering
space which is administered by the organization to which the IP
address carried in the Global Administrator subfield has been
assigned by an appropriate authority.
8. Route Origin Community
The Route Origin Community identifies one or more routers that inject
a set of routes (that carry this Community) into BGP. This is transi-
tive across the Autonomous system boundary.
The Route Origin Community is of an extended type.
The value of the high-order octet of the Type field for the Route
Origin Community can be 0x00, 0x01 or 0x02. The value of the low-
order octet of the Type field for this community is 0x03.
When the value of the high-order octet of the Type field is 0x00 or
0x02, the Local Administrator sub-field contains a number from a num-
bering space which is administered by the organization to which the
Autonomous System number carried in the Global Administrator subfield
has been assigned by an appropriate authority.
When the value of the high-order octet of the Type field is 0x01, the
Local Administrator sub-field contains a number from a numbering
space which is administered by the organization to which the IP
address carried in the Global Administrator subfield has been
assigned by an appropriate authority.
9. Link Bandwidth Community
When a router receives a route from a directly connected external
neighbor (the external neighbor that is one IP hop away), and adver-
tises this route (via IBGP) to internal neighbors, as part of this
advertisement the router may carry the bandwidth of the link that
connects the router with the external neighbor. The bandwidth of such
a link is carried in the Link Bandwidth Community.
The Link Bandwidth Community is of an extended type.
The value of the high-order octet of the Type Field is 0x00. The
value of the low-order octet of the Type field for this community is
0x04.
The value of the Global Administrator sub-field in the Value Field
MUST represent the Autonomous System of the router that attaches the
Link Bandwidth Community.
The bandwidth of the link is expressed as 4 octets in IEEE floating
point format, units being bytes per second. It is carried in the
Local Administrator sub-field of the Value Field.
10. Operations
A BGP speaker may use the Extended Communities attribute to control
which routing information it accepts or distributes to its peers.
The Extended Community attribute MUST NOT be used to modify the BGP
best path selection algorithm in a way that leads to forwarding
loops.
A BGP speaker receiving a route that doesn't have the Extended Commu-
nities attribute MAY append this attribute to the route when propa-
gating it to its peers.
A BGP speaker receiving a route with the Extended Communities
attribute MAY modify this attribute according to the local policy.
By default if a range of routes is to be aggregated and the resultant
aggregates path attributes do not carry the ATOMIC_AGGREGATE
attribute, then the resulting aggregate should have an Extended Com-
munities path attribute which contains the set union of all the
Extended Communities from all of the aggregated routes. The default
behavior could be overriden via local configuration, in which case
handling the Extended Communities attribute in the presence of route
aggregation becomes a matter of the local policy of the BGP speaker
that performs the aggregation.
If a route has a non-transitivity extended community, then before
advertising the route across the Autonomous system boundary the com-
munity SHOULD be removed from the route. However, the community
SHOULD NOT be removed when advertising the route across the BGP Con-
federation boundary.
A route may carry both the BGP Communities attribute as defined in
[RFC1997]), and the Extended BGP Communities attribute. In this case
the BGP Communities attribute is handled as specified in [RFC1997],
and the Extended BGP Communities attribute is handled as specified in
this document.
11. IANA Considerations
The value of the high-order octet of the Type Field determines if an
extended community is a regular type or an extended type. The value
of the high-order octet of the Type Field defined as regular type (or
extended type) for a extended community MUST NOT be reused as the
value of the high-order octet of the Type Field defined as extended
type (or regular type).
For the high-order octet of the Type Field, values 0x00 through 0x03
and 0x40 through 0x43 are assigned in this document and are defined
as extended types.
For the combination of the high-order and low-order octets of the
Type Field values 0x0002-0x0004, 0x0102-0x0103, and 0x0202-0x0203 are
assigned in this document.
The Type Field values 0x04-0x3f and 0x44-0x7f for regular types
(0x0400-0x3fff and 0x4400-0x7fff when expressed as extended types)
are to be assigned by IANA, using the "First Come First Served" pol-
icy defined in RFC 2434.
The extended Type Field values 0x0000-0x0001, 0x0005-0x00ff,
0x0100-0x0101, 0x0104-0x01ff, 0x0200-0x0201, 0x0204-0x02ff,
0x0300-0x03ff, and 0x4000-0x43ff are to be assigned by IANA, using
the "First Come First Served" policy defined in RFC 2434.
The Type Field values 0x90-0xbf and 0xd0-0xff for regular types
(0x9000-0xbfff and 0xd000-0xffff when expressed as extended types)
are to be assigned by IANA, using the "IETF Consensus" policy defined
in RFC2434.
The Type Field values 0x80-0x8f and 0xc0-0xcf for regular types
(0x8000-0x8fff and 0xc000-0xcfff when expressed as extended types)
are experimental, and are not to be assigned by IANA.
12. Security Considerations
This extension to BGP does not change the underlying security issues.
13. Acknowledgements
The authors would like to thank John Hawkinson, Jeffrey Haas, Bruno
Rijsman, and Alex Zinin for their suggestions and feedback.
14. References
[BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4
(BGP-4)", RFC 1771, March 1995.
[RFC1997] Chandra, R., Traina, P., Li, T., "BGP Communities
Attribute", RFC1997, August 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
15. Author Information
Srihari R. Sangli
Procket Networks, Inc.
1100 Cadillac Court
Milpitas, CA - 95035
e-mail: srihari@procket.com
Dan Tappan
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA 01824
e-mail: tappan@cisco.com
Yakov Rekhter
Juniper Networks, Inc.
1194 N. Mathilda Ave
Sunnyvale, CA 94089
e-mail: yakov@juniper.net